Integrally bladed rotor airfoil fabrication and repair techniques

ABSTRACT

The present invention relates to a method for fabricating an integrally bladed rotor which comprises providing a hub section, preferably formed from a titanium based alloy, and welding an airfoil, also preferably formed from a titanium based alloy, to the hub section. The method further comprises partially aging and cooling the hub section prior to welding and aging the airfoil and the weld joint between the airfoil and the hub section subsequent to welding. The post welding aging step is preferably carried out using a novel encapsulated local airfoil heating device having a plurality of heating elements woven into a jacket made from a high temperature cloth material. The method of the present invention may also be used to repair integrally bladed rotors.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method forfabricating/repairing an integrally bladed rotor and a novelencapsulated local airfoil heating device used in the method.

[0002] The increasing use of integrally bladed rotor hardware in large,high performance gas turbine engines is driven by the demand forimprovements in performance and efficiency. In conventional rotors,rotating airfoils are retained by dovetail slots broached into the rimof a disk. In an integrally bladed rotor, the airfoils and disk form onecontinuous piece of metal. The weight and fuel savings afforded byintegrally bladed rotors result from their ability to retain rotatingairfoils with less disk mass than would be required in a conventionallydesigned rotor. Furthermore, the reduced disk mass of an integrallybladed rotor disk permits weight reduction in other components whichreact upon or obtain a reaction from the rotors, i.e. shafts, hubs, andbearings.

[0003] In the past, a major disadvantage associated with the use ofintegrally bladed rotors in large gas turbine engines has been the lackof a reliable method for repairing integrally bladed rotor airfoils thathave been damaged beyond blendable limits. Because the airfoils areintegral with the disk, damage to airfoils beyond blendable limitsrequires the removal of the entire rotor from service and replacementwith a new integrally bladed rotor, at significant expense.

[0004] Other problems associated with integrally bladed rotors relate tothe fabrication method employed to manufacture them. They can bemachined out of a single large forging; however, this approach is notdesirable. A large forging, e.g., large billet, has lower propertycapability and a significant amount of the starting material, which canbe very expensive depending upon the material, is machined away. Also,the part is at risk of scrap out due to inevitable machining errorsduring manufacture. Another approach for manufacturing integrally bladedrotors is to attach separately forged airfoils to a rotor by a bondingprocess.

[0005] A titanium alloy consisting essentially of 6.0 wt. % aluminum,2.0 wt. % tin, 4.0 wt. % zirconium, 6.0 wt. % molybdenum, and thebalance essentially titanium is a desirable alloy for integrally bladedrotors due to its high toughness, its tensile and fatigue strength, andits good weldability. It is however a difficult alloy to process afterwelding because of the nature of the weld zone microstructure which isan orthorhombic martensite. First, the OEM friction weld must be postweld heat treated to stabilize the microstructure and relieve stresses.Secondly, the integrally bladed rotor must be able to undergo subsequentin-service weld repairs due to foreign object damage.

[0006] While weld properties can be restored with full solution plus agepost weld heat treatment, it is impractical to perform this operationdue to possible airfoil distortion and surface contamination, especiallyfor non-OEM welds. The current post weld heat treatment of 1100° F. for2-6 hours results in a very hard weld zone with low impact strengthcompared to parent metal and inadequate fatigue crack propagationcapability. The post weld heat treatment could be raised to a 1300° F.average temperature for up to two hours to restore acceptable weld zoneimpact and toughness properties; however, this treatment results in a4-6% loss in tensile strength over the baseline condition.

[0007] Such a loss is unacceptable for many highly stressed parts.

SUMMARY OF THE INVENTION

[0008] Accordingly, it is an object of the present invention to providean improved method for fabricating and/or repairing integrally bladedrotors.

[0009] It is a further object of the present invention to provide amethod which allows use of a high temperature post weld heat treatmentwhile maintaining high tensile and fatigue strength.

[0010] It is a further object of the present invention to provide anovel encapsulated local airfoil heating device to perform said hightemperature post weld heat treatment.

[0011] In accordance with a first aspect of the present invention, amethod for creating an integrally bladed rotor broadly comprisesproviding a hub section, preferably formed from a titanium based alloy,and welding an airfoil, also preferably formed from a titanium basedalloy, to the hub section. Prior to welding, the hub section and airfoilmay be solution treated, oil quenched, partially aged and cooled priorto welding. The method further comprises applying a high temperaturepost weld average heat treatment to the weld joint between the hubsection and the airfoil subsequent to welding.

[0012] A novel encapsulated local airfoil heating device is used toperform the post weld average heat treatment. The device broadlycomprises a plurality of heating elements woven into a jacket made froma high temperature cloth material. The heating device is placed over theairfoil and the weld joint to perform the post weld heat treatment.

[0013] A method for repairing integrally bladed rotors in accordancewith the present invention broadly comprises machining away a damagedportion of an integrally bladed rotor airfoil and welding an undamagedairfoil section to a remaining portion of the integrally bladed rotorairfoil. This is followed by placing the encapsulated local airfoilheating device over the undamaged airfoil and the weld and performingthe post mold heat treatment to relieve residual stresses and restoremicrostructure and mechanical properties to the weld joint and adjacentmetal.

[0014] Other details of the fabricating/repairing methods and theencapsulated local airfoil heating device, as well as other object andadvantages attendant thereto, are set forth in the following descriptionand the accompanying drawings wherein like reference numerals depictlike elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a schematic representation of an integrally bladed rotorhaving an airfoil welded to a hub section;

[0016]FIG. 2 is a schematic representation of an encapsulated localairfoil heating device in accordance with the present invention;

[0017]FIG. 3 is a schematic representation of the heating device of FIG.2 positioned over an airfoil and weld joint; and

[0018]FIGS. 4 and 5 are graphs illustrating the improvements obtainedusing the fabricating/repairing method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0019] Referring now to the drawings, FIG. 1 illustrates an integrallybladed rotor 10 having a hub section 12 and an airfoil 14 welded to thehub section along a weld joint 16 and airfoil sections 15 welded toundamaged airfoil portions 11 along weld lines 16′. FIG. 1 also showscertain airfoils 11 having damaged tip portions 19 which require repair.The hub section 12, the airfoils 14, and the airfoil sections 15 may beformed using any suitable technique known in the art. The hub section12, each of the airfoils 11, 14, and 17, and the airfoil sections 15 maybe formed from a titanium based alloy. Suitable titanium based alloysinclude a titanium based alloy consisting essentially of 6.0 wt. %aluminum, 2.0 wt. % tin, 4.0 wt. % zirconium, 6.0 wt. % molybdenum, andthe balance essentially titanium (TI-6246); a titanium based alloyconsisting essentially of 6.0 wt. % aluminum, 2.0 wt. % tin, 4.0 wt. %zirconium, 2.0 wt. % molybdenum, and the balance essentially titanium(TI-6242); and a titanium based alloy consisting essentially of 6.0 wt.% aluminum, 4.0 wt. % vanadium, and the balance essentially titanium(TI-64). While titanium alloys are preferred, the methods describedherein could be used with hub sections, airfoils, and airfoil sectionsformed from nickel based alloys such as Inco 718. The hub section 12,the airfoils 11, 14, and 17, and/or the airfoil sections 15 can beformed from the same alloy or from different alloys.

[0020] The weld joint 16 may be formed using any suitable weldingtechnique known in the art. For example, each airfoil 14 could be weldedto the hub section 12 using a friction welding technique such as OEMfriction welding.

[0021] Prior to welding, the hub section 12 and each airfoil 14 may besolution treated and oil quenched. For example, if the hub section 12and/or airfoil 14 are formed from a TI 6246 alloy, solution treatmentand oil quenching are performed. The solution treatment and oilquenching treatment may be performed by first heating the hub section 12and airfoil 14 to a temperature in the range of from about 1620° F. toabout 1655° F. for a time in the range of from about 1 hour to 4 hours.The solution and oil quenching treatment may be carried out in anelectric furnace with air or argon atmosphere. The hub section 12 and/orthe airfoil 14 may be in a suitable rack or fixture for transference toan oil tank (not shown) in a timely manner with minimal delay.Alternatively, a vacuum furnace with oil quench capability may be usedto perform the solution treatment. After the oil quenching step has beencompleted, the hub section 12 and the airfoils(s) 14 may be subjected toa partial aging treatment at a temperature in the range of from about1075° F. to about 1125° F. for a time in the range of from about 2 hoursto about 8 hours. The partial aging treatment may be carried out usingany suitable furnace known in the art having any suitable atmosphere.Following partial aging, the hub section 12 and the airfoil(s) 14 may becooled at a rate of about 40° F. to 100° F. per minute.

[0022] As mentioned before, to fabricate an integrally bladed rotor 10,each airfoil 14 is welded to the hub section 12. After welding has beencompleted, the hub section 12 and the weld joint 16 between the airfoil14 and the hub section 12 is subjected to an over-aging post weld heattreatment during which the weld joint 16 is heated to a temperature inthe range of 1275° F. to 1325° F. in an inert gas atmosphere for a timeperiod in the range of 1 to 4 hours. After the post weld heat treatment,the airfoil 14 and the weld joint 16 are cooled at a rate of from about40° F. to about 100° F. per minute.

[0023] In accordance with the present invention, the post weld heattreatment is preferably carried out using a novel encapsulated localairfoil heating device 20 such as that shown in FIG. 2. The heatingdevice 20 comprises a jacket or a sock 22 formed from a ceramicinsulating material such as a high temperature aluminoborsilicate-basedfabric. The jacket or sock 22 serves a dual purpose. First, itconcentrates heat generated by the device 20 at the airfoil surface andallows the weld joint 16 and the surrounding heat affected zone to reachand stabilize at the intended post weld heat treatment temperature.Second, the jacket 22 prevents unintentional heating of adjacentairfoils.

[0024] The device 20 has a plurality of radiant resistance heatedelements 24 woven into the fabric of the jacket 22. The heating elements24 preferably comprise high watt density heating wires.

[0025] The heating elements 24 serve to radiate heat directly to theairfoil surface. The heating elements 24 may be arranged in individuallycontrolled heating element zones. For example, the device 20 could havefour individually controlled heating element zones.

[0026] A titanium gettering sheet 26 in foil form is also woven into thefabric of the jacket 22 to prevent local atmospheric contamination andto allow further temperature control capability in the zoned heatingdevice 20.

[0027] The device 20 further includes a plurality of non-contactthermocouple wires 28 woven into the fabric of the jacket 22. Thethermocouple wires 28 are used to allow precise temperature controlduring the post weld heat treatment cycle. A variable transformer 30 isconnected to the heating elements 24 in each heating zone and suppliespower to the heating elements. The transformer 30 may be used to varythe current supplied to the heating elements 24 in each temperature zoneas a function of the temperature sensed by the thermocouple wires 28.

[0028] The device 20 is used as shown in FIG. 3 by placing the device 20over the airfoil 14 and the weld joint 16. Power is then supplied to theradiant heating elements 24 so that heat is applied to the weld joint 16at the aforesaid post weld heat treatment temperature. The power iscontinued for a time in the aforesaid post weld heat treatment timerange.

[0029] The same basic method used to fabricate an integrally bladedrotor 10 can be used to refurbish a damaged integrally bladed rotor. Torepair an integrally bladed rotor, a damaged portion 19 of a rotorairfoil 11 is first machined away using any suitable machining techniqueknown in the art. Thereafter, an undamaged airfoil section 15 is weldedto the remaining airfoil portion 11 of the integrally bladed rotorairfoil. Any suitable welding technique known in the art such as afriction welding technique may be used to weld the airfoil section 15 tothe portion 11. The undamaged airfoil section 15 may be from any of theabovementioned titanium based alloys or a nickel based alloy.

[0030] The heating device 20 is then placed over the undamaged airfoil15 and the weld joint 16′ and energized to perform the aforementionedpost weld heat treatment at a temperature in the range of 1275° F. to1325° F. for a time in the range of 1 to 4 hours in an inert gasenvironment. Following the post weld heat treatment, the undamagedairfoil 15 and the weld joint 16′ are cooled at a rate of from about 40°F. to about 100° F. per minute.

[0031] Following the post weld heat treatment, the undamaged airfoilsection 15 is machined to obtain a required geometry.

[0032] The heating device 20 of the present invention is advantageous inthat it provides focused, local heating so that adjacent airfoils andthe disk hub on the integrally bladed rotor are kept well belowtemperatures that would result in a strength debit and/or dimensionaldistortion. At the same time, the heating device 20 provides therequired temperature and time duration required for post weldment stressrelief of a superalloy airfoil material.

[0033] Referring now to FIGS. 4 and 5, the graphs illustrate how themethod of the present invention eliminates parent metal (P/M) strengthdebit and the alloy toughness matches the baseline. As shown in FIG. 4,the ultimate tensile strength, yield strength, and elongation propertiesof a Ti-6Al-2Sn-4Zr-6Mo alloy from which an integrally bladed rotor canbe formed and which has been subjected to solution treatment, oilquenching, partial aging at 1100° F. and over-aged at 1300° F. (alloyno. 1) are better as compared to the same alloy which has been solutiontreated, air cooled and aged at 1100° F. (alloy no. 2) and to the samealloy which has been solution treated, air cooled and aged at 1300° F.(alloy no. 3). FIG. 5 illustrates the effect of the method of thepresent invention on the charpy impact strength of a Ti-6Al-2Sn-4Zr-6Moalloy used for the disk section of an integrally bladed rotor.

[0034] While the heating device 20 has been described in the context oftreating integrally bladed rotors formed from a titanium based material,it can be used to treat integrally bladed rotors and airfoils formedfrom other materials such as a nickel-based superalloy.

[0035] It is apparent that there has been provided in accordance withthe present invention integrally bladed rotor airfoil fabrication andrepair techniques which fully satisfy the means, objects, and advantagesset forth hereinbefore. While the present invention has been describedin the context of specific embodiments thereof, other alternatives,modifications, and variations will become apparent to those skilled inthe art having read the foregoing description. Therefore, it is intendedto embrace such alternatives, modifications, and variations as fallwithin the broad scope of the appended claims.

What is claimed is:
 1. A method for creating an integrally bladed rotorcomprising the steps of: providing a hub section formed from a metalalloy; welding an airfoil formed from a metal alloy to said hub section;and solution treating said hub section at a temperature in the range offrom about 1620° F. to about 1655° F. for a time period in the range offrom about 1 to 4 hours and oil quenching said solution treated hubsection prior to said welding step.
 2. A method according to claim 1,further comprising partially aging said solution treated and quenchedhub section at a temperature in the range of from about 1075° F. toabout 1125° F. for a time period in the range of from about 2 hours toabout 8 hours prior to said welding step.
 3. A method according to claim2, further comprising cooling said partially aged hub section at a rateof from about 40° F. to about 100° F. per minute.
 4. A method accordingto claim 1, further comprising aging said airfoil and a weld jointbetween said airfoil and said hub section subsequent to said weldingstep at a temperature in the range of 1275° F. to 1325° F. for a timeperiod in the range of 1 hour to 4 hours.
 5. A method according to claim4, further comprising cooling said aged airfoil at a rate of from about40° F. to about 100° F. per minute.
 6. A method according to claim 4,wherein said aging step comprises placing an encapsulated local airfoilheating device over said weld joint and radiating heat directly to asurface of said airfoil.
 7. A method according to claim 6, wherein saidencapsulated local airfoil heating device has a plurality of resistanceheating elements and said aging step comprises varying electrical powerapplied to said heating elements to heat said airfoil and said weldjoint at a temperature within said temperature range.
 8. A methodaccording to claim 1, wherein said hub section and said airfoil are eachformed from a titanium alloy.
 9. A method according to claim 8, whereinsaid hub section and said airfoil are formed from the same titaniumalloy.
 10. A method according to claim 1, wherein said hub section andsaid airfoil are each formed from a titanium based alloy consistingessentially of 6.0 wt. % aluminum, 2.0 wt. % tin, 4.0 wt. % zirconium,6.0 wt. % molybdenum, and the balance essentially titanium.
 11. A devicefor performing localized heat treatment of integrally bladed rotorairfoils comprising: a jacket to be placed over said airfoil; and aplurality of heating elements woven into said jacket.
 12. A deviceaccording to claim 11, wherein said jacket is made from a ceramicinsulating material.
 13. A device according to claim 11, wherein saidjacket is formed from a high temperature aluminoborsilicate basedfabric.
 14. A device according to claim 11, wherein said heatingelements are high watt density heating wires and said jacket serves toconcentrate heat generated by said heating elements at a surface of saidairfoil and to allow a weld joint between said airfoil and a hub and aheat affected zone to reach and stabilize at a post weld heat treatmenttemperature.
 15. A device according to claim 11, further comprising amaterial which prevents unintentional heating of adjacent airfoils iswoven into said jacket.
 16. A device according to claim 15, wherein saidmaterial is a titanium getting sheet material.
 17. A device according toclaim 11, further comprising thermocouple wires woven into said jacketto control heating of said airfoil during a post weld heat treatment.18. A device according to claim 11, further comprising a variabletransformer connected to said heating elements for varying electricalpower supplied to said heating elements and airfoil temperature profile.19. A method for repairing an integrally bladed rotor airfoil comprisingthe steps of: machining away a damaged portion of said integrally bladedrotor airfoil; welding an undamaged airfoil section to a remainingportion of said integrally bladed rotor airfoil; placing an encapsulatedlocal airfoil heating device over said undamaged airfoil and a weldjoint between said undamaged airfoil and said remaining portion; andheat treating said undamaged airfoil and said weld joint using saidheating device to reduce residual stresses and restore microstructureand mechanical properties to the weld joint and adjacent metal.
 20. Amethod according to claim 19, wherein said heat treating step isperformed in an inert atmosphere.
 21. A method according to claim 19,further comprising machining a surface of said undamaged airfoil sectionto obtain a required geometry.
 22. A method according to claim 19,wherein said welding step comprises welding an undamaged airfoil sectionformed from a titanium based alloy to said remaining portion of saidintegrally bladed rotor airfoil.
 23. A method according to claim 19,wherein said heat treating step comprises aging said airfoil section ata temperature in the range of from about 1275° F. to about 1325° F. fora time period in the range of from about 1 hour to about 4 hours.
 24. Amethod according to claim 23, further comprising cooling said agedairfoil section at a rate of from about 40° F. to about 100° F. perminute.
 25. A method for creating an integrally bladed rotor comprisingthe steps of: providing a hub section formed from a metal alloy; weldingan airfoil formed from a metal alloy to said hub section; partiallyaging at least one of said hub section and said airfoil at a temperaturein the range of from about 1075° F. to about 1125° F. for a time periodin the range of from about 2 hours to about 8 hours prior to saidwelding step; and aging said airfoil and a weld joint between saidairfoil and said hub section subsequent to said welding step at atemperature in the range of 1275° F. to 1325° F. for a time period inthe range of about 1 hour to about 4 hours.
 26. A method according toclaim 25, wherein said aging step comprises placing an encapsulatedlocal airfoil heating device over said weld joint and radiating heatdirectly to a surface of said airfoil.
 27. A method according to claim26, wherein said encapsulated local airfoil heating device has aplurality of resistance heating elements and said aging step comprisesvarying electrical power applied to said heating elements to heat saidairfoil and said weld joint at a temperature within said temperaturerange.
 28. A method according to claim 25, wherein said hub section andsaid airfoil are each formed from a titanium alloy.
 29. A methodaccording to claim 25, wherein said hub section and said airfoil areformed from the same titanium alloy.
 30. A method according to claim 25,wherein one of said hub section and said airfoil is formed from atitanium based alloy consisting essentially of 6.0 wt. % aluminum, 2.0wt. % tin, 4.0 wt. % zirconium, 6.0 wt. % molybdenum, and the balanceessentially titanium and the other of said hub section and said airfoilis formed from a titanium based alloy consisting essentially of 6.0 wt.% aluminum, 4.0 wt. % vanadium, and the balance essentially titanium.31. A method according to claim 25, wherein one of said hub section andsaid airfoil is formed from a titanium based alloy consistingessentially of 6.0 wt. % aluminum, 2.0 wt. % tin, 4.0 wt. % zirconium,6.0 wt. % molybdenum, and the balance essentially titanium and the otherof said hub section and said airfoil is formed from a titanium basedalloy consisting essentially of 6.0 wt. % aluminum, 2.0 wt. % tin, 4.0wt. % zirconium, 2.0 wt. % molybdenum, and the balance essentiallytitanium.